This invention is directed to polyfunctional acrylate derivatives of caprolactone-polyols.
Polyfunctional acrylates have been used in a large number of fields including coating and elastomers. Most ultraviolet (UV) light applications are based on binders containing acrylic unsaturations. These binders are generally classified as epoxy acrylates, urethane acrylates and polyester acrylates. Glycol acrylates are also extensively used to modify UV curing systems.
Acrylate-capped polycaprolactone polyol derivatives are described in U.S. Pat. No. 3,700,643. The derivatives are described as useful in producing coating compostions that are readily cured to solid protective films. The acrylate-capped polycaprolactone compounds include those defined by the following formula: ##STR1## where Z is hydrogen or methyl, Q is the residue remaining after reaction of the caprolactone polyol and x is an integer having a value of from 1 to 4. In columns 6 and 7 the patent describes the production of mono-hydroxyl mono-acrylate-capped polycaprolactone and diacrylate capped polucaprolactone, i.e., when x in the above formula is 1 or 2. However, the acrylate-capped polycaprolactone compounds of U.S. Pat. No. 3,700,643 have high viscosity and reduced compatibility with several types of polymers. Accordingly, they have limited utility in coatings formulations.
The process employed in U.S. Pat. No. 3,700,643 produces acrylate-capped polycaprolactones which are high in viscosity, which limits their use as diluents. The process of U.S. Pat. No. 3,700,643 is conducted under a nitrogen atmosphere at elevated temperatures. When this process was repeated, gels formed due to polymerization of the acrylic acid and the acrylates which are used. In a commercial process, the excess acrylic acid is preferably removed by water washing. Using the conditions described in U.S. Pat. No. 3,700,643 emulsions formed when water was added to the reaction mixture, due to the presence of polyacrylic acid. Further, the solvent in the products from U.S. Pat. No. 3,700,643 (Example 13) was stripped off in an inert atmosphere causing an additional increase in viscosity. Finally, the process of U.S. Pat. No. 3,700,643 employs a high level of the inhibitor, phenothiazine, which remains in the product. Phenothiazine at the levels used in Example 13 would interefere with photochemical curing procedures because of the high molar absorptivity of phenothiazine.
The polyfunctional acrylate derivatives of this invention have generally lower viscosity, are thermally stable and impart toughness properties to compositions utilizing them. In particular, they are useful as polyurethane modifiers. Also, they are compatible with a number of polymers and when polymerized, improve the flexibility and toughness of the polymer. Prior art polyester polyols are high in viscosity. For example, an acrylated polyester VPS-2700 manufactured by Degussa Corporation for general radiation cured coatings has a viscosity of 8,000 to 13,000 centipoise. In addition, they are difficult to manufacture in functionalities of three or greater since the use of trifunctional monomers in polyesters lead to network structures and gels.